Marine propeller



March 23, 1963 G. ROSEN 3,082,827

MARINE PROPELLER Filed April 20, 1962 no.5 X

INVENTOR GEORGE ROSEN wwym ATTOR NEY United States Patent Ofifice3,082,827 Patented Mar. 26, 1963 3,082,827 MARINE PROPELLER GeorgeRosen, West Hartford, Conn., assignor to United Aircraft Corporation,East Hartford, Conn, a corporation of Delaware Filed Apr. 20, 1%2, Ser.No. 189,134 17 Claims. (Cl. 170-13524) This invention relates to a highspeed marine propeller particularly of the supercavitating type.

An object of this invention is a propeller construction providing theoptimum hydrodynamic shape for supercavitating propellers over thecomplete operating speed range of the propelled vehicle.

A further object is a propeller construction matching a controllablepitch and a fixed pitch pair of blade elements to provide the optimumhydrodynamic shape for a supercavit-ating marine propeller blade.

A further object is a marine supercavitating propeller constructionhaving a main blade portion pivotally mounted in a hub for pitchchanging movement and a fixed auxiliary blade portion supported by saidhub nesting with, and extending forward from the trailing edge of saidmain portion for less than half the chord of the main portion.

Other objects and advantages will be apparent from the followingspecification and the accompanying drawings in which:

FIG. 1 is a side elevation of a propeller incorporating the invention;

FIG. 2 is a view partly in section showing the relation of the main andauxiliary blades in "high pitch position;

FIG. 3 is a view similar to FIG. 2 showing the blade in low pitchposition;

FIG. 4 is a section similar to FIG. 2 showing the blade in reverse pitchposition;

FIG. 5 is a side elevation similar to FIG. 1 showing a modified form ofthe adjustable blade; and

FIG. 6 is a view similar to FIG. 2 showing a section through themodified portion of the blade.

Refinements in hydrodynamic design and the development of marinepowerplants with substantial improvements in specific weight haveadvanced the speed potential of marine vehicles several fold. This trendof increasing ship speeds has, however, introduced a number of problemsin the design of eflective marine propellers, which, unless adequatelysolved, could seriously inhibit the development of practical high-speedships and other water-borne vehicles.

It has been recognized that, with increasing range of ship speeds, thereis growing need for controllable pitch (or [at least variable pitch)marine propellers to avoid the substantial limitations on engine poweroutput inherent with the fixed pitch propeller. Also, there are theadded benefits of improved propeller efficiency at off-design conditionsand the ability to provide reverse thrust without the complexity ofsudden reversing the direction of propeller rotation.

Controllable pitch does not, however, solve the propeller cavitationproblem with its associated adverse effects on performance, noise andblade erosion. At the higher vehicle speeds, the propeller, with itsadded rot-ative speed, experiences cavitation sooner than any othercomponent of the vehicle, and it has become evident that suppression ofpropeller cavitation becomes impossible at speeds above 4050 knots, evenif the propulsion unit is lightly loaded. Consequently, there has beenactive interest in the application of supercavitating foils to marinepropellers as a means of alleviating cavitational losses. However theconsideration of a controllable pitch, supercavitating marine propellerpresents several difficult and conflicting design problems. These stemprincipally from the radical shape of the supercavitating foil.

For efiective supercavitation, it is necessary to change from theconventional foil shape with its characteristic localized pressure peaknear its blunt leading edge. At high speeds, this causes a localized,intermittent formation and collapse of. a vapor bubble which results inthe severe flow disturbance and surface erosion. A sharpedged foil will,on the other hand, produce a thin wedge shaped vapor cavity which willbe stable and not collapse until beyond the trailing edge if the foilsurface does not pierce the cavity boundary. From structuralconsiderations it is desirable to design the foil to nearly fill thecavity, and thus the characteristic shape of the supercavitating foil isa sharp leading-edge wedge. The effectiveness of this foil shape hasbeen fully substantiated experimentally. It has also been demonstratedthat for this foil shape to truly supercavitate, it must be operated atan optimum, low angle of attack to the stream direction.

In designing a controllable pitch, supercavitating marine propeller itis obviously desirable to have the blade sections of optimum foil shapeand at optimum angle of attack for its operation at the maximum designspeed of the vehicle. Although blade pitch is reduced as speed isreduced, the section angles of attack must increase above the optimumhigh speed value in order to produce enough lift to absorb engine powerat these lower speeds. With an appreciable increase in angle of attack,the flow cannot make the turn around the sharp leading edge and fiowseparation occurs on the upper surface with attendant serious loss inperformance.

Other design problems associated with the controllable pitch,supercavitating propeller stem from the poor structural characteristicsof its sharp, wedge-shaped sections. The thin leading edge has lowtorsional stiffness, and for off-design conditions where non-optimumangles of attack result in large unsteady hydrodynamic forces, it isquite susceptible to flutter. Severe leading edge damage and distortionhave been experienced on some experimental supercavitating propellers,due to this characteristic. Furthermore, the inherent blunt trailingedge of the wedgeshaped section is unfavorable from the standpoint ofmass concentration in an area where it is structurally of little benefitin a controllable pitch type blade, and yet pro duces a largecentrifugal twisting moment about the pitch change "axis of the blade.This results in a requirement for large capacity in the pitch changingmechanism of the propeller and consequent weight penalties.

The present invention is aimed at a practical solution to these designproblems in a controllable pitch supercavitating marine propeller. Thisobjective is achieved by splitting the supercavitating blade into twoelements as shown in the drawings. Element 10 becomes the controllablepitch portion of the blade and element 12 is maintained as a fixed pitchportion. FIG. 2 shows the two elements aligned for the design maximumspeed condition where in conjunction with each other they form anoptimum supercavitating blade section shape. The element -10 nests withand overlaps the element 12 which is arranged to nest with the trailingportion of the element 10. The trailing edge 14- of the composite bladeis formed primarily of the blunt edge of the element 12 and to a minorextent by the relatively sharp trailing edge of the element 10. In onepreferred embodiment the trailing edges of the two elements aresubstantially coextensive throughout the planfor-m of the element 10. As

the element spaced from but comparatively adjacent to the pitch changingaxis 18 of the movable element.

Element 12 is fixed on or secured to a hub 20 by any suitable means andmay even be integral with the hub, if desired. The movable portion 10 isrotatably mounted in the hub 20 for pitch changing movement about apitch changing axis 18 in any suitable and Well known manner. Forpurposes of illustration, it is shown as supported in a journal 22 inthe propeller hub and held therein by a flange 24. It should beunderstood that this schematic showing is for purposes of illustrationonly and that any suitable well-known mounting may be used. Any suitableand well-known mechanism may be used for changing the propeller pitch.For purposes of illustration and explanation, this mechanism is shown asa plunger 26 longitudinally movable along the axis 28 of rotation of thepropeller hub 20. A pin 38 depending from one side of the flange 24 isreceived in a transverse slot 32 in the plunger 26 and serves totransform longitudinal movements of the plunger 26 into pitch changingmovements of the element 10. The hub 20 is supported upon a shaft 34which in turn is mounted in bearings, not shown, for rotatablysupporting the propeller about the axis 28. The propeller may be drivenby an engine 36 drivingly connected with the propeller shaft 34 by gears38 and 40. The propeller pitch may be controlled by any suitable andwell-known means such as a manual control or it may be controlled by aspeed responsive governor 42 operatively connected with the plunger 26by a rod 44. The governor may be of any well-known construction andobtain its speed signal directly from the shaft 34 or from the engine36.

Although only one blade has been shown for simplicity in the drawings,it should be understood that two, three or any desired number of bladessimilar to the blade 10, 12 may be mounted in, or supported by, the hub26. As indicated above, FIG. 2 shows the elements 10, 12 nested inoverlapping relation to form in effect the single supercavitating bladein the design maximum speed condition and having a cross-section of atypical supercavitating blade with its relatively sharp leading edge andthe blunt trailing edge. The design maximum speed position is thehighest pitch position attainable in the propeller and represents theoptimum angle of attack for the blade sections at the selected highvehicle speed and the corresponding rotating speed of the propellerwhich is selected to provide the most favorable advance ratio andcavitation index at this design condition.

At lower vehicle speeds such as when accelerating from a low speed, orfrom rest, it is necessary to reduce the propeller pitch in order thatthe power absorption requirement of the propeller does not exceed themaximum power capacity of the engine and load the engine down to belowfull output. This is accomplished either with manual adjustment of bladepitch to give full engine output at any vehicle speed, or with agovernor which will automatically reduce pitch, as vehicle speed isreduced, to maintain a set engine speed at full power. As shown in FIG.3, as the element 10 turns on its pitch changing axis 18 to reduce thepropeller pitch it moves away from the fixed element 12 and leaves adivergent slot 46 between the elements having an opening 48 on the faceside of the blade. The upper or camber side 53 of the element 12 isgiven a shape extending from the relatively sharp leading edge of theelement 12 which will be generally convex and which, in conjunction withthe complementary face side 52 of the element 10 (generally concave inshape), forms a curved divergent slot for maximum turning of the flow inorder to achieve maximum lift. The curvature of the two complementarysurfaces 52 and 53 need not be identical, but will be selected toprovide the most favorable flow conditions for the low pitch positionsof the specific application, and with the sole limitation that this willnot interfere with the attainment of the desired contour of the faceside of the blade when in the design maximum speed position. The element12, being arranged at a favorable angle of attack because of the flowdirecting effect of the face surface 54 of the element 10, acts as ahigh lift device to increase the thrust and the performance of thepropeller at the lower forward speeds of the vehicle. The divergent slotacts in a manner similar to that in a slotted flap construction andassists in maintaining flow with a favorable pressure gradient over thecamber face of the element 12 and assists in preventing separation offlow on its camber surface. As the vehicle speed increases and the loadon the propeller decreases, due to the tendency to decrease the angle ofattack of the blade sections, the governor will increase the propellerpitch on element 10 in order to maintain the desired engine speed, untilthe design vehicle maximum speed is obtained. The vehicle will thus bebrought from its rest or slow speed condition to the design cruisecondition without encountering adverse angles of attack on the bladesections with accompanying flow disturbance and loss in performance.

It is often desirable to obtain reverse thrust on a marine propeller andthis is quite often done by rotating the fixed pitch type propeller in areverse direction. This might be done by reversing the engine rotationor providing a reversing gear system, either of which represents addedcomplexity and weight penalty. With the controllable type propellerdescribed herein it is possible to turn the movable element 10 to anegative pitch angle as shown in FIG. 4 and this may be done by movementof the plunger 26 either manually or by suitable governor controlmechanism as is well-known in the art. The propeller element 10 would beturned to the negative angle as shown by FIG. 4 and would largely shieldthe fixed element 12 so that its effect in trying to drive the vehicleforward would be largely nullified, whereas element 10 would produce thenormally large magnitude of reverse thrust of a conventional blade.

As indicated above, by nesting the two elements it is possible toprovide a comparatively thin trailing edge 16 for the movable element10. This would make the trailing edge considerably lighter over what itwould be if it had to include all the metal in the blunt trailing edge14 of the element 12. This is of particular advantage as far as thepitch changing mechanism is concerned. Because of the well-known actionof blade mass disposed at appreciable distance from its pitch changingaxis there is a tendency to reduce the propeller pitch by the action ofa force which may at times be considerable. This is known as thecentrifugal twisting moment and if large requires correspondingly largeforces in the pitch changing mechanism. The maintaining of a blunttrailing edge on element 12 presents no problem since this is a fixedpitch element and thus does not affect the centrifugal twisting momentcharacteristics of the element 10. As shown in FIG. 6, it may be foundadvantageous to cut back the blade width of the element 10 adjacent thehub thus further reducing the centrifugal twisting moment and stillmaintaining the effective hydrodynamic shape in conjunction with theelement 12 while allowing the camber face of the element 12 to form acontinuation of the camber face of the element 10 adjacent the hub. Thefixed trailing edge portion of element 12 provides it with adequatestructural strength and the shank portion 23 of the movable element 10can be made large enough to provide the element 10 with adequatestructural strength.

It should be understood that it is not desired to limit the invention tothe exact details of construction and operation herein shown anddescribed for various modifications within the scope of the claims mayoccur to persons skilled in the art. Having now particularly describedand ascertained the nature of this invention and in what manner the sameis to be performed, 1 claim and desire to secure by Letters Patent:

1. In a supercavitating mar-inc propeller having radially extendingblades, a hub, each blade comprising a main blade portion, having asharp leading and a sharp trailing edge, pivotally mounted in said hubfor pitch changing movements, a minor blade portion fixed on said huband having a sharp leading edge and a blunt trailing edge and nestingwith said main blade portion in the high pitch position to provide acomposite blade having a sharp leading edge and a blunt trailing edgeand providing separated blade portions with a slot between the portionsin lower pitch positions.

2. In a supercavitating marine propeller, a radially extending bladehaving a sharp leading edge and a blunt trailing edge, said blade formedof a radially pivoted section and a fixed section, said fixed sectionhaving a sharp leading edge and a blunt trailing edge formingsubstantially the entire trailing edge of said blade and extending lessthan half the chord Width of said blade from said blade trailing edgetoward the pivotal axis of said radially pivoted section.

3. In a supercavitating propeller having a blade with a design conditionproducing substantially stable cavitation over the chordwise length ofthe blade, means maintaining favorable lift/ drag relations atoff-design conditions comprising means reducing the pitch of a portionof the blade including substantially the entire camber surface, andmeans maintaining a portion of the blade including the rear portion ofthe face of the blade in fixed position, to receive fluid directed bythe remainder of the face of said blade, and form a diverging slotbetween the two blade portions.

4. A blade as claimed in claim 3 in which the pitch reducing bladeportion has its major thickness adjacent the longitudinal center lineand tapers toward the leading and trailing edges and the fixed portionhas its major thickness at the trailing edge.

-5. A blade as claimed in claim 3 in which the two blade portionsoverlap and nest to form a single blade section in the high pitchposition of the blade.

6. In a supercavitating propeller, a hub, a plurality of bladesradiating from said hub, each blade comprising a rear section formedintegral with said hub, and a movable section extending forward of andoverlapping said integral section and pivotally supported by said hub onan axis forward of said integral section.

7. In a marine propeller, a hub, blades radiating from said hub, eachblade designed to have a stable cavitating layer at design conditions onits camber surface, means to reduce the blade pitch to prevent seriousflow disturbance at speeds less than the design speed and a high liftdevice associated with said blade comprising a fixed blade section fixedwith respect to said hub and nesting with said blade at designconditions, and forming a diverging slot with the trailing portion ofthe face side of said blade at said reduced pitch.

8. In a supercavitating marine propeller, a hub, blades radiating fromsaid hub, each blade comprising a controlla-ble pitch portion and afixed portion having a chord less than half the chord of thecontrollable portion and having a trailing edge substantiallycoextensive in planform with the trailing edge of the controllableportion and nesting with said controllable portion in the high pitchposition to form essentially a unitary blade and separated from saidcontrollable portion by a diverging slot at lower pitch positions, saidfixed portion having a relatively sharp leading edge and a relativelythick trailing edge.

9. In a supercavitating marine propeller, a hub, blades radiating fromsaid hub, each blade comprising a main blade portion pivotally mountedin said hub adjacent the blade center line for pitch changing movementsand a fixed auxiliary blade portion supported by said hub, nesting withthe face side of, and extending forward from the trailing edge of, saidmain portion for less than half the chord of the main portion, to aposition downstream of the pivotal of said main portion.

10. In a supercavitating marine propeller as claimed in claim 9, anauxiliary blade portion having a chord 30% to 40% of the chord of themain blade portion.

11. A marine propeller as claimed in claim 7 including means responsiveto the speed of the propeller for controlling the pitch of thepropeller.

12. In a supercavitating marine propeller, a hub, blades radiating fromsaid hub, each blade having a sharp leading edge portion and a blunttrailing edge portion and having an optimum pitch angle and shape fordesign speed conditions, each blade comprising an adjustable portionextending the full chord of the blade and a fixed portion supported bythe hub and extending less than half of the chord of the blade from thetrailing edge of the blade, on the face side, means for moving saidadjustable portion in a pitch reducing direction relative to the hub andthe fixed portion to reduce the pitch of the movable portion, and openup a divergent slot between said portions, said fixed portion having asharp leading edge and a shape to present a blade section to flowdirected by the face of said movable portion in its reduced pitchposition to provide a high lift device.

13. In a supercavitating propeller blade having a mov able portionextending the entire chord Width of the blade at the outer section buttapering inward to less than the entire chord Width of the blade at theinner section, a fixed portion having a camber side nesting with theface side of the trailing section of the movable portion and having asharp leading edge and a blunt trailing edge extending the entire lengthof the blade trailing edge, said camber side forming a supercavitatingblade section extension of said movable section in the inner section ofthe blade.

14. High lift mechanism for a supercavitating propeller comprising ablade having a movable portion forming substantially the entire camberface of the blade, a fixed portion nesting with the face of said movableportion and forming a portion of the trailing section of the face of theblade when the two portions are nested, and forming a high lift devicefor said blade when the movable portion is moved away from nestingposition.

15 Means for improving the performance of an adjustable pitch,supercavitating propeller comprising a blade having a movable portionpivoted on a pitch changing axis for pitch changing movement and formingsubstantially the entire camber face of the blade, and a fixed portionnesting with the trailing section of the face side of said movableportion and forming a minor portion of the face of said blade, saidmovable portion trailing sectionmovable on its pitch changing axis, in apitch reducing direction, away from said fixed portion, to provide ahigh lift structure with the fixed section having a shape forming adiverging slot and a high lift member with said movable section.

16. A hub, an adjustable pitch supercavitating propeller blade pivotallysupported by said hub and having a split trailing section, said splitsection comprising a flap section forming a portion of the face of saidblade and fixed With respect to said hub and having a sharp leading edgeand a blunt trailing edge and having a chord width less than half theblade chord width, the remainder of said blade pivoted to move towardand away from said flap section in pitch changing movements to open andclose a diverging slot opening on the face side of said blade anddischarging between the trailing edge of said blade and said flapsection.

'17. A propeller as claimed in claim 9 in which the maximum bladethickness of both the blade and the auxiliary blade portion is at theirrespective trailing edges.

References Cited in the file of this patent UNITED STATES PATENTS1,344,496 Flattum June 22, 1920 2,145,805 Ring Jan. 31, 1939 2,982,361Rosen Dec. 19, 1958

1. IN A SUPERCAVITATING MARINE PROPELLER HAVING RADIALLY EXTENDINGBLADES, A HUB, EACH BLADE COMPRISING A MAIN BLADE PORTION, HAVING ASHARP LEADING AND A SHARP TRAILING EDGE, PIVOTALLY MOUNTED IN SAID HUBFOR PITCH CHANGING MOVEMENTS, A MINOR BLADE PORTION FIXED ON SAID HUBAND HAVING A SHARP LEADING EDGE AND A BLUNT TRAILING EDGE AND NESTINGWITH SAID MAIN BLADE PORTION IN THE HIGH PITCH POSITION TO PROVIDE ACOMPOSITE BLADE HAVING A SHARP LEADING EDGE AND A BLUNT TRAILING EDGEAND PROVIDING SEPARATED BLADE PORTIONS WITH A SLOT BETWEEN THE PORTIONSIN LOWER PITCH POSITIONS.